The best evidence indicates men's testosterone tends to DEcrease with age.
It's important to look at the quality of the sources.
I don't think the sources in the OP are of the highest quality. Nor is the one used by PoloHoleSet! They're OK. But the Harman study HC_ uses is better - the "Confounds and validation" shows the effort they went to to ensure they had good data. It's peer reviewed. It's published.
Looking further, I found a review article which states,
Testosterone levels also decrease with age as rapidly as 0.4–2%
annually after age 30 years [Harman et al. 2001; Kaufman and
Vermeulen, 2005; Wu et al. 2008], with 35% of men in the seventh
decade having lower testosterone levels than younger men [Vermeulen
and Kaufman, 1995], and 13% of older age men meeting diagnostic levels
Reading between the lines that follow, it seems like there's a needle being threaded - are the authors avoiding directly stating that if it's a normal part of aging, it can't be justified as medically necessary but lots of money is spent on T, so let's find a way to tell practitioners how to diagnose low T as a disease that merits treatment? Can't say. It's a matter of opinion. They later say, there's a "vast literature of known and proven benefits of testosterone normalization" but also quote the FDA saying ‘The benefit and safety of TRT/[testosterone replacement therapy] medications have not been established for the treatment of low testosterone levels due to aging, even if a man’s symptoms seem related to low testosterone.’
Hard to make any hard fast conclusions, given meta-analysis identified publication bias between industry-sponsored and unsponsored trials of testosterone supplementation!